Blow-Forward autocannon Project X-ACS

[SEAKING9006]

My next project after the Airburst system, and maybe a bunch of identical mortars for mass-fire, will be a Blow-forward Autocannon. It will use a single piston, and one sprinkler valve to actuate it, and another to shut off air flow to the primary tank when the piston is in the forward position to reduce air waste and to more easily re-seat the piston. When the piston is in the rear position, the airflow control valve (between primary and secondary tanks) will be open. When the piston is moving forward and reaches the point where the rear inlet on the sleeve is open, a roller switch will disengage, closing the air inlet valve and firing valve. The inlet hole on the piston sleeve will continue to allow pressurized air to push the piston forward. The air escapes through the barrel when the forward inlet reaches the inlet on the sleeve. Air escapes, and the spring returns the piston to it's rearward position. The rear inlet hole is not closed until the last possible moment to further aid re-seating of the piston. The moment the piston's rear inlet is sealed, the roller switch re-engages, allowing the inlet valve and firing valve to open again. In order to allow the cannon to have a reasonable rate of fire, the primary tank will be kept as small as possible while still allowing a reasonable muzzle velocity. The secondary air tank Will be kept at a higher pressure and will have a preset regulator installed just before the valve, also to ensure better air use. The tank will be constantly connected to a compressor. The finished gun will be to large and awkward to use as a handheld cannon. It's final construction and operation will be similar to the Browning M2.


EDIT 6/29 :I've compiled a data file on the bolt/piston, mainly the piston head that will be bearing the force of the air pressure. I generated a list of force outputs at various pressures, specifically 5psi intervals staring at 10psi going up to 60psi. If I plan on going higher I can easily add additional intervals, which may be the case, since I plan on using my Dad's compressor (33 gallon 135psi max) as opposed to my own (3 gallon 120psi max).

I have located a number of parts from McMaster-Carr that should reduce the amount of work. Ill post one of the springs I've found, (McMaster Part Number 96485K125) because since it just about PERFECTLY fits over 1 1/4" PVC and might help others build their projects.


EDIT 7/15: After returning from a weeklong vacation, a more in-depth development schedule has been worked out. Next time I go to Home Depot/Lowe's, I will get all the fittings and pipe required for the airburst launcher, as well as a few extra fittings and ball valves, to build a proof-of-concept, manually actuated prototype of the valve. It will be fairly small, and will operate at fairly low pressure (5-10psi), with the valve actuated by ball valves. If it works, it will prove that my proposed valve is a workable design.


Things I still need to work out;
1: Where to get the proper springs. (Completed)
2: What fittings to use and how to modify to allow access to internals. (Partially Completed)
3: Draw a to-scale diagram of entire system.


EDIT: This project has been moved back behind other ones, which are more readily able to be completed. These projects will help develop some of the skills and techniques required for this concept. This decision was also compounded by the lack of availability of large-scale pressure rated fittings.

If anyone can give me any tips about properly securing pipe that runs THROUGH the fittings rather than into them, that would be GREATLY appreciated.

[VH_man]

hmm. very much like the inner workings of a Smart Parts Ion.......

If you can get the precise timing that needs to function, it will work... well.... like an Ion. wich isnt too shabby

[SEAKING9006]

I actually designed it so I WOULDN'T have to be very precise. It's the electronics that will really matter as far as timing is concerned. That's the beauty of it. And, I'm gonna put iron sights on it. It's gonna be freakin' sweet.

[VH_man]

well, i think youll find these things are much harder than youd think... but hey, take a go at it!

I think you might find sprinkler valves do not close as fast as this design requires. Might i reccomened a Direct-Acting Solenoid? Your idea involving the electronic valve shut-off is relatively ingenious.

[SEAKING9006]

Actually, the valves shutting shouldn't be that much of a problem. If that ends up being a problem, I can make the valves shut sooner. Besides, I'm trying for a relatively standard rate of fire, (4-7 r.p.s.) so off timing on the closing valves shouldn't be a problem. It wont affect the firing as long as it closes before the piston returns to the original position. The firing valve is actually connected directly to the primary tank, so when the air vents through the rear inlet, it will vent right back into the tank, and out the barrel.

[Mr.Sandman]

that going to cost an arm or two. but you should use a quick disconnect incase something goes wrong. personally i would never build and auto cannon because semi is good enough for me. but with your design it should work nicely. one more thin, autocannons have feeding problems a lot of the time so make sure it is serviceble. but good job and good luck


holy crap i need to learn how to spell

[SEAKING9006]

I'm building an autocannon because semi auto by nature is slightly more complicated to do. Autocannon mechanics can be timed by intervention by electronic devices. Semi-auto, however, most of the time is controlled by mechanical tolerances. Trigger size, sear thickness, ect. I don't feel like slaving over a dremel for half an hour, put it in, find it's too thick, take it apart, and repeat. I have been juggling a design for a striker-fired semi auto rifle in my head, though.

[psycix]

I doubt if you will, but if you get it to work then you did one damn good job.
The "green valve" should open and close very fast, if not, even your electronic timings cant help much.

[MaxuS the 2nd]

I don't feel like slaving over a dremel for half an hour, put it in, find it's too thick, take it apart, and repeat.

But this is spudding in a nutshell.

[SEAKING9006]

I don't feel like slaving over a dremel for half an hour, put it in, find it's too thick, take it apart, and repeat.

But this is spudding in a nutshell.

Didn't seem that way with the CA1, though!

[MrCrowley]

The CA1 was mostly standard parts of the shelf if I remember correctly. As you progress with more powerful cannons with new features, not everything can be bought of the shelf.

If you don't think you can stand 30 minutes on a dremel, you should stick to sprinkler valved cannons.

[SEAKING9006]

Already got that in mind, especially since I prefer electronic control. Most of my cannons should use a sprinkler valve for at least something. But yeah, 30 minutes on a dremel is nothing. But, I could use a better drill press.

[jackssmirkingrevenge]

As you progress with more powerful cannons with new features, not everything can be bought of the shelf.

And even if it can, there's no excuse to "roll your own", so to speak

[psycix]

Indeed, custom parts can always be better then factory made parts. If you got the tools and the knowledge you can build anything, but then better.
Mostly due to the fact that many parts are not made for spudding, and thus your homemade part is optimized for its purpose in your gun.

[iknowmy3tables]

that hole can't vent the pilot completely, it will just vent enough so the bolt can move back enough to close the hole, but not all the way. don't even think about making the hole longer because thats irrational, when you open the valve the bolt would not move and the air would just vent out the hole

get rid of the hole in the pilot and replace the valve in the back with a 3way 2position valve